The invention generally relates to blood processing systems and methods.
Today people routinely separate whole blood by centrifugation into its various therapeutic components, such as red blood cells, platelets, and plasma.
Certain therapies transfuse large volumes of blood components. For example, some patients undergoing chemotherapy require the transfusion of large numbers of platelets on a routine basis. Manual blood bag systems simply are not an efficient way to collect these large numbers of platelets from individual donors.
On line blood separation systems are today used to collect large numbers of platelets to meet this demand. On line systems perform the separation steps necessary to separate concentration of platelets from whole blood in a sequential process with the donor present. On line systems establish a flow of whole blood from the donor, separate out the desired platelets from the flow, and return the remaining red blood cells and plasma to the donor, all in a sequential flow loop.
Large volumes of whole blood (for example, 2.0 liters) can be processed using an on line system. Due to the large processing volumes, large yields of concentrated platelets (for example, 4xc3x971011 platelets suspended in 200 ml of fluid) can be collected. Moreover, since the donor""s red blood cells are returned, the donor can donate whole blood for on line processing much more frequently than donors for processing in multiple blood bag systems.
Nevertheless, a need still exists for further improved systems and methods for collecting cellular-rich concentrates from blood components in a way that lends itself to use in high volume, on line blood collection environments, where higher yields of critically needed cellular blood components like platelets can be realized.
As the operational and performance demands upon such fluid processing systems become more complex and sophisticated, the need exists for automated process controllers that can gather and generate more detailed information and control signals to aid the operator in maximizing processing and separation efficiencies.
The invention provides blood processing systems and methods that separate whole blood into red blood cells and a plasma constituent within a rotating centrifugal separation device. The systems and methods convey whole blood into the separation device through an inlet path including a pump operable at a prescribed rate. The systems and methods remove plasma constituent from the separation device through an outlet path including a pump operable at a prescribed rate.
According to the invention, the systems and methods derive a value Hb representing an apparent hematocrit of whole blood entering the separation device, where:       H    b    =                    H        rbc            ⁡              (                              Q            b                    -                      Q            p                          )                    Q      b      
and where Hrbc is a value relating to hematocrit of red blood cells in the separation device.
In a preferred embodiment, the systems and methods generate a control command based, at least in part, upon Hb. In one implementation, the control command recirculates at least a portion of plasma constituent for mixing with whole blood conveyed into the separation device. In another implementation, the control command controls Qb.
In a preferred embodiment, the systems and methods generate an output based, at least in part, upon Hb. In one implementation, the output comprises a value xcex7 representing efficiency of separation in the separation device, where:   η  =            Q      p                      (                  1          -                      H            b                          )            ⁢              Q        b            
In a preferred embodiment, the value Hrbc represents apparent hematocrit of red blood cells in the separation device, where:       H    rbc    =      1    -                  (                              β                          g              ⁢                              xe2x80x83                            ⁢              A              ⁢                              xe2x80x83                            ⁢              κ              ⁢                              xe2x80x83                            ⁢                              S                Υ                                              ⁢                      (                                          q                b                            -                              q                p                                      )                          )                    1                  k          +          1                    
where:
qb is inlet blood flow rate (cm3/sec), which when converted to ml/min, corresponds with Qb,
qp is measured plasma flow rate (in cm3/sec), which, when converted to ml/min corresponds with Qp,
xcex2 is a shear rate dependent term, and Sy is a red blood cell sedimentation coefficient (sec) and xcex2/Sy=15.8xc3x97106 secxe2x88x921,
A is the area of the separation device (cm2),
g is the centrifugal acceleration (cm/sec2), which is the radius of the separation device multiplied by the rate of rotation squared xcexa92 (rad/sec2), and
k is a viscosity constant=0.625, and xcexa k is a viscosity constant based upon k and another viscosity constant xcex1=4.5, where:   K  =                                          k            +            2                    α                ⁡                  [                                    k              +              2                                      k              +              1                                ]                            k        +        1              =    1.272  
In a preferred embodiment, the systems and methods operate free of any a sensor to measure blood hematocrit either in the separation device or in the inlet path.
In a preferred embodiment, the systems and methods recirculate at least a portion of plasma constituent from the separation device at a prescribed rate QRecirc for mixing with whole blood conveyed into the separation device. In this embodiment, the systems and methods control QRecirc to achieve a desired hematocrit Hi for whole blood conveyed into the separation device as follows:       Q    Recirc    =            [                                    H            b                                H            i                          -        1            ]        xc3x97          Q      b      
The various aspects of the invention are especially well suited for on line blood separation processes.
Other features and advantages of the invention will become apparent from the following description, the drawings, and the claims.